Traditional Japanese wood-block printing (called "moku hanga"). Somehow printing presses, stamps, crimps, embossing, and other physical imprinting techniques have always fascinated me. When I was 10 I carved my initials in some cork and tried to make a stamp, but I got my letters mirror-imaged. ha. Source: "Sky Print" on clay matrix by Annie B, woodblockdreams, Blogger.com.